The present invention relates to an apparatus for the detection of localized anomalies or other localized features in wood, such as knots, splits, voids, checks, and localized decay for the purpose of grading or cutting wood products such as lumber, and specifically to an apparatus employing ultrasonic energy to characterize both dried and undried wooden members. The wooden members may be trees, logs, beams, planks, lumber, boards or wood composites and the like.
Ultrasound has been used to characterize the gross properties of wooden members through measurement of time of flight, attenuation, and attenuation as a function of frequency (broadband ultrasonic attenuation) of ultrasound passing through a wooden member. For example, U.S. Pat. No. 5,307,679 to Ross and assigned to the United States of America, describes the use of ultrasonic measurements to detect a proclivity of a wooden members to degrade during the drying process. Another example includes identifying naturally occurring defects to aid in lumber grading for both structural and non-structural applications.
It is also desirable to detect, identify and locate smaller anomalies in wooden members such as knots, checks and splits. Such defects, when identified, can be input to commercially available optimization systems to allow for the sorting or cutting of the wooden members in a way so as to maximize their value, for example, by cutting a log to produce the maximum number of board feet of clear or higher grade lumber.
Traditionally identification of defects and other features affecting lumber grade has been performed visually, for example, by a saw operator visually inspecting the log or board prior to determining the necessary cross or rip cuts that will yield the best product output or yield. Recently a number of electronic scanning systems have been produced using cameras and lasers to automate this visual process. Such optical techniques are limited to the detection of superficial defects in the wooden members and even these techniques may be defeated by dirt, bark, stain or other markings on the outside of the log. More importantly, internal defects are generally not visible externally, yet may affect product performance or value.
What is needed is an apparatus for detecting and identifying localized anomalies even internal to a wooden member, that is also robust against the harsh environment of a typical sawmill or the like and that is safer, less costly and more compact than instruments based on x-rays or other electromagnetic radiation, or which provide information which those systems have difficulty in detecting such as splits and checks.